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Posted: November 29, 2009

Discovery may help manage nanoparticle wastes from consumer products

(Nanowerk News) A new understanding about nanoparticle behaviour in sewage treatment plants could improve the environmental management of nanoparticle wastes from foods, cosmetics, medicines, cleaning and personal care products.

Experts believe some nanoparticles may have harmful effects on the environment or human health, and research is currently being directed at understanding the issues involved. Scientists from the Centre for Ecology & Hydrology (CEH) and the Science and Technology Facilities Council's Isis Neutron Source, along with colleagues from King's College London and Oxford University, studied how certain nanoparticles behave in wastewater and have now identified a way to potentially help remove them during primary sewage treatment.

Identifying and managing silica nanoparticles through the sewage system.

The scientists examined silica nanoparticles, over one million tonnes of which are used in the manufacture of consumer products each year, with a large proportion of these subsequently washed down drains into sewage systems. This makes sewage treatment plants a major gateway for nanoparticles entering the aquatic environment.

The new study, details of which are published in Environmental Science & Technology ("Fate of Silica Nanoparticles in Simulated Primary Wastewater Treatment"), simulated primary sewage treatment to show that coating silica nanoparticles with a detergent-like material (called a surfactant) made the nanoparticles interact with components of the sewage to form a solid sludge. This sludge can be separated from the wastewater and disposed of. In contrast, uncoated nanoparticles stayed dispersed in the wastewater and were therefore likely to continue through the effluent stream and potentially on into the environment.

Dr Helen Jarvie from CEH, the lead author of the study, said the research proved that the surface chemistry of nanoparticles influenced their likely removal during primary sewage treatment. "By adding a coating which modifies that surface chemistry, it may be possible to re-route their journey through sewage treatment plants," she explained.

The scientists used the ISIS Neutron Source to view the sewage at the nanometre scale. Nanoparticles are too small to be seen by the human eye but the ISIS Neutron Source, acting like a giant microscope, allows scientists to study objects 1,000 times thinner than a human hair. The neutrons easily penetrate the sewage and scatter strongly from the nanoparticles, allowing the aggregation behaviour of the nanoparticles to be measured through time.

Dr Steve King from the ISIS Neutron Source said the research showed that primary sewage treatment may not be effective at removing some nanoparticles. "However," he added, "we now know where those nanoparticles may go and how we might deal with them."

Further work is now planned to examine the behaviour of a wider range of nanoparticles, with different classes of surfactants, in wastewaters.

Source: Centre for Ecology & Hydrology

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